Unnerving news from Brazil, now hosting travelers from all over the world because of the World Cup: The virus that causes polio has been found in sewage in one of the cities where matches are being played.

The World Health Organization, which announced the finding on Monday, says the virus was discovered last week in a sample collected in March at Viracopos International Airport in Campinas, which is about 60 miles outside Sao Paulo, and is where many of the World Cup teams have been landing. The agency said no cases of polio have been identified and there is no evidence the disease has been transmitted.

Genetic sequencing of the virus—the WHO didn’t say, but probably done by the Centers for Disease Control and Prevention in Atlanta—revealed that it was closely related to a poliovirus that recently caused a case of the disease in Equatorial Guinea in West Africa. Humans are polio’s only host; so that probably means the virus was carried into Brazil by a traveler, likely someone who never knew he was harboring it.

Brazil, like most of the rest of the world, continues to vaccinate against polio, even though there have been no cases of polio in Brazil since 1989, and the Americas were declared polio-free in 1991. The high vaccination rate — 95 percent of children nationwide, and higher than that in Sao Paulo State — kept the virus from spreading.